Human polyomavirus type BK (BK virus) is a non-enveloped virus with a circular, double-stranded-DNA genome of about 5,300 bp. BK virus was first recognized as a member of the polyomavirus family in 1971, after isolation from the urine of a renal-transplant recipient. Subsequent studies documented a worldwide rate of seroprevalence in adults of more than 80 percent. Typically, primary infection with the BK virus occurs during childhood by the respiratory route, followed by latency of the virus in the urogenital tract. Asymptomatic reactivation and intermittent shedding of virus in the urine occur spontaneously in immunocompetent persons but are more frequent among those with altered cellular immunity, such as pregnant women, patients with cancer who are receiving chemotherapy, HIV-1 infected individuals and recipients of renal or other allografts. Overt clinical disease from BK virus infection is rare and is clearly linked to the degree of immunosuppression.
BK-virus associated nephropathy has become an increasingly recognized cause of renal dysfunction in renal transplant patients. According to retrospective studies, BK virus nephropathy develops in 1 to 5 percent of renal-transplant recipients, with loss of allograft function occurring in as many as 45 percent of the affected patients. Although BK virus-specific antiviral therapy is not available, in some cases, BK virus replication may be controlled by reducing the level of maintenance immunosuppression. Recent evidence suggests that detection of BK virus DNA closely follows the course of BK virus nephropathy and may serve as a noninvasive tool for diagnosis and monitoring. Therefore, quantification of BK virus load in renal transplant patients would be useful both for diagnosing BK virus nephropathy and for monitoring the response to therapy, i.e., reduction in immunosuppression. In addition, BK virus has been implicated in other diseases, such as prostate cancer.
Accordingly, there remains a need for the development of reliable diagnostic tests to detect BK virus with a sensitivity that allows detection of low titers of virus, as well as for detection of different BK virus genotypes. In addition, there remains a need for a reliable diagnostic test to distinguish between BK virus and other polyoma viruses, such as JC virus. Such assays are critical to prevent transmission of the virus through blood and plasma derivatives or by close personal contact. The present invention addresses these needs.